To load a propane gas truck, the gas truck is usually driven onto a loading platform or a loading pad adjacent a large storage or supply tank. A pair of hoses, one being a liquid hose and the other being a return hose, are pulled from the storage tank and coupled to the tank carried by the gas truck. Once the gas truck's tank has been filled, the hoses are uncoupled from the tank carried by the truck and the gas truck is driven away.
Over the years, there have been numerous accident caused by the driver driving the gas truck from the loading station without uncoupling both hose nozzles from the vehicle tank. This happens despite established procedure that most gas distribution businesses have established to protect the safety of the driver, people in the vicinity, and the environment. For example, many gas businesses insist that the driver block or chock the gas truck wheels on the passenger side before attaching the hose nozzles to the vehicle tank. Also, the driver is instructed to pass around the rear of the gas truck when he or she is to remove the chock from the vehicle wheel. Thus, if the driver in fact follows this procedure, he will most likely note that there remains one or more hose nozzles coupled to the vehicle tank. But past accidents have shown that drivers do not always follow these procedures and that these procedures are not foolproof. Even in spite of the many precautions that are given to drivers and despite set procedures as set forth above, there are still situations where serious accidents have been caused by the driver driving the gas truck away from the loading station while one or more hose nozzles remains coupled to the vehicle tank. In many cases, the result of a gas truck driving away while a hose nozzle is coupled to the vehicle tank is that a valve or other part of the vehicle tank is pulled or broken from the tank causing gas to spill out onto the loading station and in and around the storage tank. This presents a very dangerous situation because any type of spark or fire can set off a large explosion and fire.
Therefore, there exists a need for a foolproof system that will assure that a gas truck cannot be driven away from a storage tank while one or more gas hoses are coupled to the vehicle tank.